Nigeria has the 2nd highest number of people living with HIV (PLWH) and the most pediatric HIV infections globally, however, it has been neglected as a focus of public health efforts. Progress towards UNAIDS 90-90- 90 goals in Nigeria has been slow with all goals < 35%. Youth and men who have sex with men (MSM), are the weakest link in Nigeria's response to the HIV epidemic. Interventions reaching youth (including hard-to-reach MSM) and improving HIV care outcomes across the HIV care continuum should involve combination interventions as these have additive benefits compared to single interventions. In this study, we propose to build on infrastructure developed through a very successful U.S-Nigeria HIV-centered academic partnership in collaboration with partner institutions in Ibadan, Lagos and Jos, Nigeria. We will test two combination interventions among youths aged 15 to 24 years across the HIV care continuum. In the UG3 phase, we will (Aim 1) develop manualized interventions for: (a) HIV testing and linkage; and (b) HIV care outcomes among youth age 15-24 years in Ibadan using a combination approach that includes theoretically-grounded peer navigation and mHealth components. Once developed we will (Aim 2) test each combination intervention in pilot trials in Ibadan for feasibility, acceptability and initial efficacy using a pre-post design. The two interventions include: 2a) social media engagement + peer navigation to improve HIV testing and linkage to care among young MSM. The pilot test for this intervention will be considered successful if there is an increase of ? 30% in the number of young men completing HIV tests and an increase in the HIV incidence rate by OR=2.0 over a 48-week period compared to baseline. In addition, we will pilot test: 2b) a short message service (SMS; via adaptation of an evidence-based intervention, TXTXT) + peer navigation intervention to improve HIV care outcomes (e.g. care retention, ART adherence and viral suppression) among 40 young PLWH. This pilot intervention will be considered successful if there is ? 30% increase in proportion with viral load < 1000 copies/mL over a 48-week period, reflecting an effect size of OR=1.5 compared to baseline. We will also assess feasibility for measurement of medication adherence (via ART concentration in hair) and retention in care (via medical records abstraction). In the UH3 phase we will (Aim 3) demonstrate the scalability and efficacy of the two combination interventions in different HIV seroprevalence settings in Nigeria by: 3a) conducting a randomized stepped wedge trial (5 steps, 6 sites) in Ibadan, Lagos and Jos; and 3b) testing ART adherence and retention in care as mediators AND age, gender, and mode of transmission as potential moderators of the HIV care intervention effect. We hypothesize that, using the same primary outcome measures as in the UG3, the effect size of each combination intervention across and within settings, will be ? the effects observed in the UG3. Our goal is to develop efficacious and scalable combination intervention strategies that will accelerate UNAIDS 90/90/90 goals among Nigerian youths, including MSM.